Whether it's for an art piece or simply to preserve a perfect posterior, creating a plaster cast of a woman's behind is something you can accomplish with the help of a willing model and some common art store supplies. This article will teach you to create a plaster mold that can be used to form a perfect replica of a derriere (or any other body part).

Steps

Method1

Preparing to Make the Cast

1

Purchase plaster bandages that are approved to use on skin. Plaster bandages can be purchased from art stores, or in large quantities from a hospital supply store[1]. Plaster bandages are made to be used in body casting[2], unlike traditional Plaster of Paris powder or similar materials, which can be extremely dangerous.[3]

You can buy plaster casting kits that include lubricant and sometimes a drop cloth. Many are marketed toward pregnant women to cast their bellies, but it will work fine for your purposes.[4]

Trim the bandages to about 8 inches (200 mm) in length so they will be easier to work with.[5]

If the bandages are wide (6 inches or more), fold them in half lengthwise. You'll have an 8x3 inch double layer of bandage to work with.[6]

2

Set up your workspace. You'll want a hard surface, like a tile floor or sturdy table, for your model to stretch out and hold a stable position. Avoid rooms with carpeting--the plaster will ruin the carpet if there are any spills or drips. Place a waterproof drop-cloth over the area where you will be working. If your model is going to be on a table, you may want to spread a tarp on the table and the floor beneath. This will protect your furniture and make cleanup a snap.[7]

Make sure you have access to a shower or bath so the model can rinse off after you have removed the caste.[8]

Check the temperature of the room. If you can control the heat, you will want the room to be very warm so your model doesn't get cold when she disrobes. If you don't have access to the temperature controls, bring in a space heater to create a suitable environment.[9]

If you use a tarp to cover your workspace, look for one with some texture. It can become very slippery when wet and may make it difficult for your model to hold her pose.[10]

3

Help your model feel comfortable. She might feel nervous or embarrassed at first, so it's important to run through the process with her beforehand. Knowing what to expect may ease her mind and increase her confidence. Let her know you will halt the process at any time if she begins to feel uncomfortable.[11] Your model's comfort and safety should be your first concern.

Keep things professional, but don't be cold. You will be spending a lot of time with her, and she will be in a vulnerable position, so it is essential you develop a good rapport.[12]

Have the model try out the pose you want to for the cast. She can decide if it's a pose she can hold for 30 minutes, and you can see if it's really the pose you want or if you need to make any adjustments.[13]

4

Ask the model to undress when she's ready. It is very difficult to remove dried plaster from fabric, so she may want to disrobe entirely.[14] Otherwise, she may want to wear an old bra or bikini top or an old t-shirt she can roll up so it doesn't interfere with the cast, but still keeps her chest and shoulders covered and warm.

If your model is still concerned about getting cold, she can wear socks, leg warmers, or a knit hat, too, since these areas are nowhere near the area you will be casting.

Your clothes will likely get covered with plaster, so make sure you're wearing something you plan to throw out or don't mind ruining.

Method2

Making the Negative Cast or Mold

1

Cover the skin you plan to cast with a thick layer of petroleum jelly or olive oil.[15] Allow the model to apply the lubricant between her legs and anywhere else she might not feel comfortable with you touching.[16] It is important to have a barrier between the skin and the bandages, as this will keep hair and skin from sticking to the plaster, making it painful to remove.

After your model finishes with the petroleum jelly, apply a thick layer over the back of her upper thighs, her buttocks, and her lower back (or as high as you want the cast to reach).[17]

Make sure the coat of petroleum jelly is smooth and there aren't any long hairs poking out.

Your model may wish to shave or trim her pubic hair before you begin, just to make sure nothing gets caught in the plaster.

For extra protection, your model can use a plastic wrap to cover her her anus and labia, protecting them from the wet plaster.[18]

2

Position your model on the table and provide adequate support.[19] If the pose requires her to prop herself up on her elbows, put pillows underneath her chest so she has some support. If one leg must be lifted slightly, use a phonebook to prop the leg up.

If you pose her in too difficult or uncomfortable a position, you may be forced to stop before the plaster has dried. Try to find a pose that fits your artistic vision and takes her comfort into consideration, too.[20]

3

Dip the bandages in a large bowl of warm water, one at a time. Do not leave the bandages in the water to soak--the plaster will come off and the bandages won't stick. Slide the wet bandage between your middle and index finger to wipe off excess water. Be careful not to wipe off the plaster as well.[21]

Make sure the water is warm so it will be less shocking when you place it on your model's skin.[22]

It is quite helpful to have an assistant wetting the plaster bandages and handing them to you, as you will have to work very quickly once the process has begun.

Don't let the water get too white or milky with plaster, or your bandages may separate later.[23]

4

Start from the thighs and begin laying strips down one at a time, overlapping and working your way up the body.[24] You must work as quickly and efficiently as possible, as the plaster becomes stiff in under 10 minutes and new strips will no longer adhere to the dried bandages.[25]

Lay down your strips in different directions, either alternating between horizontal and vertical, or in criss-crossing diagonals. This will make it less likely your cast will have holes or leaks.[26]

Use your hands to gently smooth any air bubbles out and releasing them from the sides of the bandage.[27]

Don't press too hard on the wet bandages or you may create dimples that will affect your finished mold.[28]

5

Layer the bandages as you go. Instead of covering the entire area with bandages and then starting again with a second layer, you want to be covering each area with at least three layers as you move up the body. Let the different layers criss-cross and weave over each other so the cast will be tightly sealed, strong, and firm.[29]

To prevent the edges from breaking when you remove the cast, make the edges at least six layers thick.[30]

6

Allow the plaster to harden. This should take no more than 10 or 15 minutes, and you can begin cleaning up while you wait.[31]

Tap the cast gently to test if it has hardened--it will sound firm and will feel dry.[32]

7

Loosen the edges of the dried cast, then gently lift it off the model's body. The cast will be difficult to remove--there will still be tiny hairs stuck in the plaster, despite the petroleum jelly.[33] Though it feels hard, the cast is actually quite delicate, so be very careful as you lift it.[34]

Ask the model to wiggle slightly, as this may help loosen the plaster from her skin.[35]

Make sure you have a robe or clean, dry clothes for the model to put on immediately.

8

Let the cast continue to dry. To avoid damaging the mold, you can place it on a soft surface, with the hollow side down.[36] You can also tie a string around the cast and hang it from a hangar or a nail in the wall.[37]

Cover the completely dried cast with an oil-based varnish to strengthen it and prevent mold.[38]

Once dry, your plaster mold is ready for use.

Method3

Making the Positive or Final Cast

1

Inspect the inside of the cast for any holes or cracks that might allow plaster to escape when you pour it the mold.[39] Repair these cracks by smoothing them over with a little wet plaster or clay.

Use sandpaper to buff away any ragged edges or bumps.

You may want to file the top, bottom, and sides of the cast so they are even and represent the exact area of the body you wish to mold. So if you accidentally placed the bandages too high on your model's back, you can now file the plaster back down.

2

Spray the inside of the cast with oil soap. This will create a barrier between the plaster cast and the liquid plaster, allowing you to remove your sculpture with ease.[40]

3

Mix up a few pounds of plaster in a large bucket. You'll have to estimate the amount it will take to fill the cast. Make sure you follow the directions on the package.[41]

Pour the powder plaster into the bucket and then add water, mixing vigorously[42]

Scrape the bottom and sides of the bucket so that all the powder is incorporated into the water and you have no lumps.[43]

4

Place your plaster cast on a flat surface or somewhere it will remain steady while you pour the mold. You want the freedom to tip it slightly so you can distribute the filling evenly, but you don't want it to tip over, either.[44] Try placing it on the ground, hollow side up, and wrapping an old blanket around it for a little support.

5

Pour the liquid plaster into the cast. Pour slowly, as this will decrease the chance of air bubbles. Gently shake the cast and tap the bottom of the cast to release any air bubbles that may have formed.[45]

6

Allow the plaster to harden for at least 30 minutes. It will heat up significantly as it dries. You'll know it's ready when it's once again at room temperature.[46]

Only test the temperature of the plaster when it has clearly hardened, so you don't get any on your skin.

7

Remove the plaster from the mold. You can smooth any creases, rough edges, or lumps with sandpaper. Paint or display the finished cast as you see fit.